1. Field of the Invention
The present invention relates to a keyboard switch of an electronic equipment, and more particularly to a keyboard switch having a rectangular actuation key of a high rectangle ratio.
2. Description of the Prior Art
Various structures have been used in the prior art keyboards of electronic equipments. They are classified into two major categories, one in which a plurality of key switches are arranged and the other in which a plurality of switch patterns are arranged on a printed circuit board and the switch patterns are selectively shorted by depressing keys arranged on the switch patterns. In those structures, the keys are normally biased by springs oppositely to the depression direction, and when the key is to be actuated, it is depressed against the biasing force.
A space key or a shift key of a full keyboard for a typewriter or a computer uses a rectangular key having a rectangle ratio of larger than 1.5. If an end area of such a key is depressed, a rotating moment is created by the biasing force and thus, the key is subject to both the depression force and a force which tends to incline a key shaft provided at center of the key. As a result, if the key switch is arranged at the center of the rectangular key under the key, the keyboard will not be smoothly operated or may be broken during long term use. To avoid the above problem, a torsion bar structure shown in FIGS. 1 and 2 has been used in the prior art rectangular key. FIG. 2 shows a sectional view taken along a line A--A of FIG. 1.
In FIGS. 1 and 2, numeral 10 denotes a known key switch which is fixed to a mounting hole 51 of a keyboard chassis 50 by a flange 14 and a pawl 15. Precise positioning is done by a positioning projection 12 provided at a bottom of the flange 14, which positioning projection is fitted to a positioning hole of the keyboard chassis 50. A terminal 11 is provided at a bottom of the key switch 10 and is soldered to a printed circuit board 60.
A rectangular key 20 is fitted to a stem 13 formed at the top of the key switch 10. Only the key 20 projects from an equipment case, not shown. Torsion bar receptacles 21 are formed at a bottom of the key 20. Ends of a U-shaped torsion bar 30 engage with the torsion bar receptacles. The torsion bar 30 is slidably mounted on a bearing 40 mounted on the keyboard chassis 50. In the structure shown, the key switch 10 contains a biasing mechanism and the torsion bar 30 merely mechanically engages the ends of the key 20.
In this arrangement, when one end of the key 20 is depressed, the depression force is transmitted to the other end through the torsion bar 30. Therefore, smooth operation is assured and the key 20 is not inclined or tilted and forces tending to dislodge or break the key switch 10 and the stem 13 are not created.
However, the above arrangement needs the keyboard chassis 50 for mounting the key switch and the torsion bar and hence it is complex in construction, takes a long time to assemble. As a result, the cost of the equipment increases and compactness and lightness of the equipment are compromised.